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From Genes to Genetic Diseases: What Kinds of Mutations Matter?
Abstract Our genes are made up of hundreds to millions of building blocks, called DNA nucleotides, and if just a single nucleotide of DNA becomes mutated it might cause a devastating genetic disease. But sometimes a mutation actually does no damage. What kinds of mutations have to occur to cause a genetic disease? In this science project, you will explore online genetic databases to identify how a mutation in a gene can result in a dysfunctional protein, and how other mutations may have no effect at all. Objective Determine why some gene mutations cause genetic diseases, but others do not. Materials and Equipment *Computer with an Internet connection *Lab notebook Introduction The Human Genome Project has estimated that the human genome contains around 20,000 to 25,000 genes. Each of these genes is made up of hundreds to millions of DNA nucleotides. Sometimes only a single DNA mutation (change in the DNA sequence) can cause a person to have a devastating genetic disease, and researchers have been able to identify mutations responsible for causing thousands of different genetic diseases and conditions. But sometimes a DNA mutation may do no harm at all. It all has to do with what the DNA mutation is and where it is located. Every gene in the human body consists of DNA (deoxyribonucleic acid). DNA is a genetic code that is made up of four different types of nucleotides: adenine (A), thymine (T), guanine (G), and cytosine ©. This DNA code is turned into RNA (ribonucleic acid) in our bodies in a process called transcription. In RNA, a nucleotide called uracil substitutes for every thymine. The RNA then goes through a process called translation to turn into amino acids. During translation, every three RNA nucleotides code for a single amino acid. This set of three nucleotides is called a "codon," and different codons may code for the same amino acid. In the end, a sequence of DNA has been turned into a sequence of amino acids joined together in a long chain, which is called a protein. Proteins are responsible for most of the functions of our cells. Many things can happen during this process to prevent a gene from turning into protein or to have a non-functional protein created. In a gene, if a single DNA nucleotide is mutated, for example from an adenine (A) to a guanine (G), this may cause the wrong amino acid to be made. If the wrong amino acid is made and assembled into a long chain of amino acids, the resulting protein may not work. This is because different amino acids are different in many ways, such as size and in the electric charges they have. These different characteristics affect how they interact with each other as well as the other molecules that surround them (such as other amino acids and water). For example, positively and negatively charged molecules prefer to interact with each other and with water, which is called being'hydrophilic', whereas nonpolar molecules do not like to interact with charged molecules or with water, which is called being hydrophobic. These seemingly small differences can have very large consequences. For example, in cystic fibrosis there is a mutation in a gene, called the CFTR gene, that encodes for a channel that controls the flow of particles in cells. Specifically, this channel normally regulates whether small negatively charged particles, called chloride ions, can flow into, or flow out of, the cells. The movement of charged particles acts to balance the flow of water into, and out of, the cells. In people with cystic fibrosis, the mutated CFTR gene creates a channel that does not function, and consequently the flow of water in tissues is abnormal. In turn, the abnormal flow of water causes a build up of thick mucus on the lining of many internal organs and can have many other devastating effects on different parts of the body (see Figure 1 below). While DNA mutations clearly cause a number of genetic diseases, some DNA mutations may not be problematic. In this science project, you will investigate cystic fibrosis and the genetic mutations that cause it, using online genetic databases. This investigation will allow you to determine what type of mutations may alter the function of a protein and which ones may have little or no effect. Terms and Concepts *Genes *DNA *Mutation *Genetic disease *Nucleotides *RNA *Transcription *Translation *Amino acids *Codon *Hydrophilic *Hydrophobic *Allele Questions *How does a gene become a protein? *In a given gene, what kind of DNA mutation would not change the protein that is made? *What makes some amino acids hydrophobic and others hydrophilic? *How common are mutations in the human genome? Is it very likely or very unlikely that your DNA carries any mutations? Photos Category:Genetics and genomics Experiment